Documenting Camera LayoutBy Ethan Ace, Published Oct 22, 2012, 08:00pm EDT
Documenting camera layouts can be important:
- Ensuring that you have a realistic field of view that covers the area you want with the sufficient coverage
- Understanding what gaps in coverage you might have and where there are overlaps
- Selecting the most appropriate resolution and lenses
- Communicating the layout to customers, partners and installers.
Inside this note, we examine each of these four key factors.
Realistic Field of View
The first benefit of performing a camera layout is that it provides a realistic representation of the camera's field of view. Often, even seasoned designers make the mistake of picturing the FOV as a cone capturing everything in front of a camera. This is incorrect, however. For example, see this image taken from one video design tool:
As shown, the camera's FOV does not begin until a distance from the camera, which differs depending on focal length, mounting height, and angle of downtilt. It also begins to drop off at the far end of the field of view, cutting off the tops of objects.
Also shown in this image, represented by the red, yellow, and green sections, are pixels per foot measurements. This allows users to set PPF targets (in this case 60, 40, 20, and 10) and see where these pixels per foot requirements fall in the camera's field of view. Some programs perform this automatically, while others show only PPF at a single target range, or none at all.
Gaps in Coverage
Providing a record of camera positions and FOV helps to visualize actual intended coverage. Though camera locations are often determined prior to the layout being created, illustrating them on a floorplan or map makes it easier to see areas which are not covered, but should be, or where there may be large overlaps in coverage, making another location preferable. Without this step, the ony way to see gaps may be to wait for the system to be installed, potentially requiring costly change orders as cameras are repositioned.
This sample site plan shows the FOVs of cameras covering a parking area:
Note the overlap shown in the two top cameras, in this case a positive, as they cover each other's blind spots. Also shown is a gap in coverage of a few parking spots at the top of the lot. This may or may not be a problem, depending on if 100% coverage is required.
Resolution and Lens Selection
By providing a visual representation of the camera's field of view, including pixels per foot measurements, users can see the effects various lenses and resolution have. This helps to ensure that cameras are not specified with a higher resolution than necessary, which wastes bandwidth and storage space, but also helps to ensure needed PPF are met.
This image illustrates the lens focal length and resolution controls in one tool, alongside other performance and positioning options:
Further, the ability to visualize the effects differing focal lengths have on the field of view can prevent unforeseen issues. Stock lenses, for example, might not provide long enough focal length to capture needed video, resulting in additional costs for third-party lenses. Visualizing the estimated field of view may prevent these costly assumptions.
The final benefit of camera layout documentation is communication of intended locations and fields of view to other parties involved. This has two key benefits:
- Internal communication: This documentation may be shared with all members on the project team, so staff, from sales to technicians, are all working with the same assumptions. This helps to prevent confusion and ensure projects are installed as intended.
- External communication: Camera layouts may also be used as a sales tool, in order to communicate the design to the customer. This may help to create buy-in, as the customer can visually see what he is (and is not) getting. This helps to protect the installing company from making changes without additional charges should the customer expect something different from the plan.
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